Various methods have been used for making complex aspheric optical surfaces, particularly for Schmidt corrector plates used in Schmidt-Cassegrain telescopes and Schmidt cameras. Various techniques have been proposed involving the drawing of the glass blank into contact with a die surface to facilitate reproduction to high accuracy. Illustrative of two of such methods are U.S. Pat. No. 3,837,124 granted Sept. 24, 1974 to Thomas J. Johnson and John F. O'Rourke, and U.S. Pat. No. 3,837,125 granted Sept. 24, 1974 to Thomas J. Johnson, both patents directed to a vacuum deformation technique using a configured die surface.
In Johnson U.S. Pat. No. 3,837,124, a two piece Schmidt corrector plate die assembly comprises a glass block and a thin glass die plate optically contacted therewith and having the inverse of the desired curve. This die plate is produced by first grinding and polishing a glass blank to the desired figure, locating its optical center, optically contacting this plate to a solid block with the central axis of the plate coinciding with the rotational axis of the block, and vacuum deforming a third glass piece onto this combination. This third glass piece is then ground and polished to become the inverse die plate in the master die.
Johnson U.S. Pat. No. 3,837,125 uses a thick one piece master die which itself is ground and polished to a curve inverse to that of the desired curve, rendering testing of the curve somewhat involved as test corrector plates must be produced therefrom for testing as the surface is being figured. The configuration of these test plates must be optically analyzed and the apparent corrections to the figure of the master die estimated. Then these corrections must be figured into the master die. If any changes are desired in the production plates which would necessitate refiguring the master die, this indirect testing procedure must be repeated.
Accordingly, it is an object of this present invention to provide a novel and relatively facile method for producing complex aspheric optical surfaces efficiently and accurately.
It is also an object to provide such a method wherein a one piece master die is used to make inversely curved die plates and is relatively rugged and is figured to the curve to be produced, thus facilitating direct optical testing.
Another object is to provide an apparatus for use in such a method.